package Assignment_2_Classes;
import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * This class represents a NTP message, as specified in RFC 2030.  The message
 * format is compatible with all versions of NTP and SNTP.
 *
 * This class does not support the optional authentication protocol, and
 * ignores the key ID and message digest fields.
 * 
 * For convenience, this class exposes message values as native Java types, not
 * the NTP-specified data formats.  For example, timestamps are
 * stored as doubles (as opposed to the NTP unsigned 64-bit fixed point
 * format).
 * 
 * However, the contructor NtpMessage(byte[]) and the method toByteArray()
 * allow the import and export of the raw NTP message format.
 * 
 * 
 * Usage example
 * 
 * // Send message
 * DatagramSocket socket = new DatagramSocket();
 * InetAddress address = InetAddress.getByName("ntp.cais.rnp.br");
 * byte[] buf = new NtpMessage().toByteArray();
 * DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 123);
 * socket.send(packet);
 * 
 * // Get response
 * socket.receive(packet);
 * System.out.println(msg.toString());
 * 
 *  
 * This code is copyright (c) Adam Buckley 2004
 *
 * This program is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU General Public License as published by the Free 
 * Software Foundation; either version 2 of the License, or (at your option) 
 * any later version.  A HTML version of the GNU General Public License can be
 * seen at http://www.gnu.org/licenses/gpl.html
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT 
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for 
 * more details.
 * 
 * 
 * Comments for member variables are taken from RFC2030 by David Mills,
 * University of Delaware.
 * 
 * Number format conversion code in NtpMessage(byte[] array) and toByteArray()
 * inspired by http://www.pps.jussieu.fr/~jch/enseignement/reseaux/
 * NTPMessage.java which is copyright (c) 2003 by Juliusz Chroboczek
 * 
 * @author Adam Buckley
 */
public class NTPMessage
{
  /**
   * This is a two-bit code warning of an impending leap second to be
   * inserted/deleted in the last minute of the current day.  It's values
   * may be as follows:
   * 
   * Value     Meaning
   * -----     -------
   * 0         no warning
   * 1         last minute has 61 seconds
   * 2         last minute has 59 seconds)
   * 3         alarm condition (clock not synchronized)
   */
  public byte leapIndicator = 0;
  
  
  /**
   * This value indicates the NTP/SNTP version number.  The version number
   * is 3 for Version 3 (IPv4 only) and 4 for Version 4 (IPv4, IPv6 and OSI).
   * If necessary to distinguish between IPv4, IPv6 and OSI, the
   * encapsulating context must be inspected.
   */
  public byte version = 3;
  
  
  /**
   * This value indicates the mode, with values defined as follows:
   * 
   * Mode     Meaning
   * ----     -------
   * 0        reserved
   * 1        symmetric active
   * 2        symmetric passive
   * 3        client
   * 4        server
   * 5        broadcast
   * 6        reserved for NTP control message
   * 7        reserved for private use
   * 
   * In unicast and anycast modes, the client sets this field to 3 (client)
   * in the request and the server sets it to 4 (server) in the reply. In
   * multicast mode, the server sets this field to 5 (broadcast).
   */ 
  public byte mode = 0;
  
  
  /**
   * This value indicates the stratum level of the local clock, with values
   * defined as follows:
   * 
   * Stratum  Meaning
   * ----------------------------------------------
   * 0        unspecified or unavailable
   * 1        primary reference (e.g., radio clock)
   * 2-15     secondary reference (via NTP or SNTP)
   * 16-255   reserved
   */
  public short stratum = 0;
  
  
  /**
   * This value indicates the maximum interval between successive messages,
   * in seconds to the nearest power of two. The values that can appear in
   * this field presently range from 4 (16 s) to 14 (16284 s); however, most
   * applications use only the sub-range 6 (64 s) to 10 (1024 s).
   */
  public byte pollInterval = 0;
  
  
  /**
   * This value indicates the precision of the local clock, in seconds to
   * the nearest power of two.  The values that normally appear in this field
   * range from -6 for mains-frequency clocks to -20 for microsecond clocks
   * found in some workstations.
   */
  public byte precision = 0;
  
  
  /**
   * This value indicates the total roundtrip delay to the primary reference
   * source, in seconds.  Note that this variable can take on both positive
   * and negative values, depending on the relative time and frequency
   * offsets. The values that normally appear in this field range from
   * negative values of a few milliseconds to positive values of several
   * hundred milliseconds.
   */
  public double rootDelay = 0;
  
  
  /**
   * This value indicates the nominal error relative to the primary reference
   * source, in seconds.  The values  that normally appear in this field
   * range from 0 to several hundred milliseconds.
   */ 
  public double rootDispersion = 0;
  
  
  /**
   * This is a 4-byte array identifying the particular reference source.
   * In the case of NTP Version 3 or Version 4 stratum-0 (unspecified) or
   * stratum-1 (primary) servers, this is a four-character ASCII string, left
   * justified and zero padded to 32 bits. In NTP Version 3 secondary
   * servers, this is the 32-bit IPv4 address of the reference source. In NTP
   * Version 4 secondary servers, this is the low order 32 bits of the latest
   * transmit timestamp of the reference source. NTP primary (stratum 1)
   * servers should set this field to a code identifying the external
   * reference source according to the following list. If the external
   * reference is one of those listed, the associated code should be used.
   * Codes for sources not listed can be contrived as appropriate.
   * 
   * Code     External Reference Source
   * ----     -------------------------
   * LOCL     uncalibrated local clock used as a primary reference for
   *          a subnet without external means of synchronization
   * PPS      atomic clock or other pulse-per-second source
   *          individually calibrated to national standards
   * ACTS     NIST dialup modem service
   * USNO     USNO modem service
   * PTB      PTB (Germany) modem service
   * TDF      Allouis (France) Radio 164 kHz
   * DCF      Mainflingen (Germany) Radio 77.5 kHz
   * MSF      Rugby (UK) Radio 60 kHz
   * WWV      Ft. Collins (US) Radio 2.5, 5, 10, 15, 20 MHz
   * WWVB     Boulder (US) Radio 60 kHz
   * WWVH     Kaui Hawaii (US) Radio 2.5, 5, 10, 15 MHz
   * CHU      Ottawa (Canada) Radio 3330, 7335, 14670 kHz
   * LORC     LORAN-C radionavigation system
   * OMEG     OMEGA radionavigation system
   * GPS      Global Positioning Service
   * GOES     Geostationary Orbit Environment Satellite
   */
  public byte[] referenceIdentifier = {0, 0, 0, 0};
  
  
  /**
   * This is the time at which the local clock was last set or corrected, in
   * seconds since 00:00 1-Jan-1900.
   */
  public double referenceTimestamp = 0;
  
  
  /**
   * This is the time at which the request departed the client for the
   * server, in seconds since 00:00 1-Jan-1900.
   */
  public double originateTimestamp = 0;
  
  
  /**
   * This is the time at which the request arrived at the server, in seconds
   * since 00:00 1-Jan-1900.
   */
  public double receiveTimestamp = 0;
  
  
  /**
   * This is the time at which the reply departed the server for the client,
   * in seconds since 00:00 1-Jan-1900.
   */
  public double transmitTimestamp = 0;
  
  /**
   * Constructs a new NtpMessage from an array of bytes.
   */
  public NTPMessage(byte[] array)
  {
    // See the packet format diagram in RFC 2030 for details 
    leapIndicator = (byte) ((array[0] >> 6) & 0x3);
    version = (byte) ((array[0] >> 3) & 0x7);
    mode = (byte) (array[0] & 0x7);
    stratum = unsignedByteToShort(array[1]);
    pollInterval = array[2];
    precision = array[3];
    
    rootDelay = (array[4] * 256.0) + 
      unsignedByteToShort(array[5]) +
      (unsignedByteToShort(array[6]) / 256.0) +
      (unsignedByteToShort(array[7]) / 65536.0);
    
    rootDispersion = (unsignedByteToShort(array[8]) * 256.0) + 
      unsignedByteToShort(array[9]) +
      (unsignedByteToShort(array[10]) / 256.0) +
      (unsignedByteToShort(array[11]) / 65536.0);
    
    referenceIdentifier[0] = array[12];
    referenceIdentifier[1] = array[13];
    referenceIdentifier[2] = array[14];
    referenceIdentifier[3] = array[15];
    
    referenceTimestamp = decodeTimestamp(array, 16);
    originateTimestamp = decodeTimestamp(array, 24);
    receiveTimestamp = decodeTimestamp(array, 32);
    transmitTimestamp = decodeTimestamp(array, 40);
  }
  
  
  
  /**
   * Constructs a new NtpMessage in client -> server mode, and sets the
   * transmit timestamp to the current time.
   */
  public NTPMessage()
  {
    // Note that all the other member variables are already set with
    // appropriate default values.
    this.mode = 3;
    this.transmitTimestamp = (System.currentTimeMillis()/1000.0) + 2208988800.0; 
  }
  
  
  
  /**
   * This method constructs the data bytes of a raw NTP packet.
   */
  public byte[] toByteArray()
  {
    // All bytes are automatically set to 0
    byte[] p = new byte[48];
    
    p[0] = (byte) (leapIndicator << 6 | version << 3 | mode);
    p[1] = (byte) stratum;
    p[2] = (byte) pollInterval;
    p[3] = (byte) precision;
    
    // root delay is a signed 16.16-bit FP, in Java an int is 32-bits
    int l = (int) (rootDelay * 65536.0);
    p[4] = (byte) ((l >> 24) & 0xFF);
    p[5] = (byte) ((l >> 16) & 0xFF);
    p[6] = (byte) ((l >> 8) & 0xFF);
    p[7] = (byte) (l & 0xFF);
    
    // root dispersion is an unsigned 16.16-bit FP, in Java there are no
    // unsigned primitive types, so we use a long which is 64-bits 
    long ul = (long) (rootDispersion * 65536.0);
    p[8] = (byte) ((ul >> 24) & 0xFF);
    p[9] = (byte) ((ul >> 16) & 0xFF);
    p[10] = (byte) ((ul >> 8) & 0xFF);
    p[11] = (byte) (ul & 0xFF);
    
    p[12] = referenceIdentifier[0];
    p[13] = referenceIdentifier[1];
    p[14] = referenceIdentifier[2];
    p[15] = referenceIdentifier[3];
    
    encodeTimestamp(p, 16, referenceTimestamp);
    encodeTimestamp(p, 24, originateTimestamp);
    encodeTimestamp(p, 32, receiveTimestamp);
    encodeTimestamp(p, 40, transmitTimestamp);
    
    return p; 
  }
  
  
  
  /**
   * Returns a string representation of a NtpMessage
   */
  public String toString()
  {
    String precisionStr =
      new DecimalFormat("0.#E0").format(Math.pow(2, precision));
   //String time1 = timeToString(transmitTimestamp);
   //String time2 = timeToString(originateTimestamp);
    return 
      "T1 = " + timestampToString(originateTimestamp) + "\n" +
      "T2 = " + timestampToString(receiveTimestamp);
  }
  
  
  
  /**
   * Converts an unsigned byte to a short.  By default, Java assumes that
   * a byte is signed.
   */
  public static short unsignedByteToShort(byte b)
  {
    if((b & 0x80)==0x80) return (short) (128 + (b & 0x7f));
    else return (short) b;
  }
  
  
  
  /**
   * Will read 8 bytes of a message beginning at <code>pointer</code>
   * and return it as a double, according to the NTP 64-bit timestamp
   * format.
   */
  public static double decodeTimestamp(byte[] array, int pointer)
  {
    double r = 0.0;
    
    for(int i=0; i<8; i++)
    {
      r += unsignedByteToShort(array[pointer+i]) * Math.pow(2, (3-i)*8);
    }
    
    return r;
  }
  
  
  
  /**
   * Encodes a timestamp in the specified position in the message
   */
  public static void encodeTimestamp(byte[] array, int pointer, double timestamp)
  {
    // Converts a double into a 64-bit fixed point
    for(int i=0; i<8; i++)
    {
      // 2^24, 2^16, 2^8, .. 2^-32
      double base = Math.pow(2, (3-i)*8);
      
      // Capture byte value
      array[pointer+i] = (byte) (timestamp / base);
      
      // Subtract captured value from remaining total
      timestamp = timestamp - (double) (unsignedByteToShort(array[pointer+i]) * base);
    }
    
    // From RFC 2030: It is advisable to fill the non-significant
    // low order bits of the timestamp with a random, unbiased
    // bitstring, both to avoid systematic roundoff errors and as
    // a means of loop detection and replay detection.
    array[7] = (byte) (Math.random()*255.0);
  }
  
  
  
  /**
   * Returns a timestamp (number of seconds since 00:00 1-Jan-1900) as a
   * formatted date/time string. 
   */
  public static String timestampToString(double timestamp)
  {
    if(timestamp==0) return "0";
    
    // timestamp is relative to 1900, utc is used by Java and is relative
    // to 1970 
    double utc = timestamp - (2208988800.0);
    
    // milliseconds
    long ms = (long) (utc * 1000.0);
    
    // date/time
    String date = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss").format(new Date(ms));
    
    // fraction
    double fraction = timestamp - ((long) timestamp);
    String fractionSting = new DecimalFormat(".000000").format(fraction);
    
    return date + fractionSting;
  }
  
  public static String timeToDouble(double timestamp, double timestamp2)
  {
    //if(timestamp==0) return "0";
    
    // timestamp is relative to 1900, utc is used by Java and is relative
    // to 1970 
    double utc = timestamp - (2208988800.0);
    double utc2 = timestamp2 - (2208988800.0);
    
    // milliseconds
    long ms = (long) (utc * 1000.0);
    long ms2 = (long) (utc2 * 1000.0);
    // time
    String time = new SimpleDateFormat("HH:mm:ss").format(new Date(ms));
    String time2 = new SimpleDateFormat("HH:mm:ss").format(new Date(ms2)); 
    
    // fraction
    double fraction = timestamp - ((long) timestamp);
    String fractionString = new DecimalFormat(".000000").format(fraction);
    double fraction2 = timestamp2 - ((long) timestamp2);
    String fractionString2 = new DecimalFormat(".000000").format(fraction2);
    
    String finalTime = time + fractionString;
    String finalTime2 = time2 + fractionString2;
    
    //timestamp breakup
    String hours = finalTime.substring(0,2);
    int hour = Integer.parseInt(hours);
    
    String minutes = finalTime.substring(3,5);
    int minute = Integer.parseInt(minutes);
    
    String seconds = finalTime.substring(6,8);
    int second = Integer.parseInt(seconds);
    
    String milis = finalTime.substring(9);
    int mili = Integer.parseInt(milis);
    
    //timestamp2 breakup
    String hours2 = finalTime2.substring(0,2);
    int hour2 = Integer.parseInt(hours2);
    
    String minutes2 = finalTime2.substring(3,5);
    int minute2 = Integer.parseInt(minutes2);
    
    String seconds2 = finalTime2.substring(6,8);
    int second2 = Integer.parseInt(seconds2);
    
    String milis2 = finalTime2.substring(9);
    int mili2 = Integer.parseInt(milis2);
    
    //doing the subtraction
    int finalHour = hour - hour2;
    int finalMinute = minute - minute2;
    int finalSec = second - second2;
    int finalMili = mili - mili2;
    
    String timeDiff = finalHour + ":" + finalMinute + ":" + finalSec + "." + finalMili;
    
    return timeDiff;
  }
  
   
  
  /**
   * Returns a string representation of a reference identifier according
   * to the rules set out in RFC 2030.
   */
  public static String referenceIdentifierToString(byte[] ref, short stratum, byte version)
  {
    // From the RFC 2030:
    // In the case of NTP Version 3 or Version 4 stratum-0 (unspecified)
    // or stratum-1 (primary) servers, this is a four-character ASCII
    // string, left justified and zero padded to 32 bits.
    if(stratum==0 || stratum==1)
    {
      return new String(ref);
    }
    
    // In NTP Version 3 secondary servers, this is the 32-bit IPv4
    // address of the reference source.
    else if(version==3)
    {
      return unsignedByteToShort(ref[0]) + "." +
        unsignedByteToShort(ref[1]) + "." +
        unsignedByteToShort(ref[2]) + "." +
        unsignedByteToShort(ref[3]);
    }
    
    // In NTP Version 4 secondary servers, this is the low order 32 bits
    // of the latest transmit timestamp of the reference source.
    else if(version==4)
    {
      return "" + ((unsignedByteToShort(ref[0]) / 256.0) + 
                   (unsignedByteToShort(ref[1]) / 65536.0) +
                   (unsignedByteToShort(ref[2]) / 16777216.0) +
                   (unsignedByteToShort(ref[3]) / 4294967296.0));
    }
    
    return "";
  }
}   